This invention relates generally to airfoils for gas turbine engines, and specifically to turbine vane airfoils. In particular, the invention concerns a turbine vane airfoil configured for turning flow, for example in a transition duct region between high and low pressure section of the turbine.
The gas turbine engine is a power generation system built around a compressor, a combustor and a turbine, which are arranged in flow series with a forward (upstream) inlet and an aft (downstream) exhaust. The compressor compresses air from the inlet, which is mixed with fuel in the combustor and ignited to produce hot combustion gases that drive the turbine, and then are exhausted downstream. Compressed air is also utilized to cool downstream engine components, particularly turbine and exhaust parts exposed to hot working fluid flow.
The turbine is coupled to the compressor via a common shaft or, in larger-scale designs, via a series of coaxially nested shaft spools. Each spool operates at a different pressure and rotational speed, and employs a number of different stages comprised of alternating rotor blades and stator vanes. The rotor blades and stator vanes (generically, “turbine blades”) have airfoil surfaces configured to compress incoming air from the inlet, and to extract rotational energy from the hot working fluid in the turbine.
In ground-based industrial gas turbines, power output is typically provided in the form of rotational energy, which is transferred to a shaft and used to drive a rotating mechanical load such as an electrical generator. Because weight is not as great a factor in ground-based applications, industrial gas turbines can be quite large, and utilize complex spooling systems for increased efficiency.
In some configurations, the compressor stages are centrifugal, rather than axial-flow, and can be either directly or indirectly coupled to the turbine shafts. Ground-based turbines are also commonly configured for combined-cycle operations, in which additional energy is extracted from the partially-cooled exhaust gas stream, for example by driving a steam turbine.
Aviation applications include turbojet, turbofan and turboshaft engines. Most modem fixed-wing aircraft employ a two- or three-spool turbofan configuration, as opposed to the older turbojet design. Rotary-wing aircraft (i.e., helicopters) typically utilize turboshaft engines, which deliver energy primarily in rotational form. Turbofan engines, on the other hand, drive a forward fan or ducted propeller to generate thrust via a bypass flow directed around the main engine core. Most turbofans are directly driven by the low-pressure spool, but some advanced designs utilize a reduction gearbox for independent speed control, reducing fan noise and increasing efficiency.
Subsonic aircraft typically employ high-bypass turbofans, in which most of the thrust is generated from the bypass flow and the exhaust generates relatively lower specific thrust, as compared to low-bypass turbofans with higher specific thrust. The engine core also provides power for accessory functions such as pneumatics, hydraulics and environmental control, for example via a bleed air system, an electrical generator, or both.
Auxiliary power units (APUs), which are essentially small gas turbine engines, are also utilized for accessory power. Auxiliary power units are variously configured for ground operations, when the main engines are not turning, as emergency in-flight backups, for independent full-time operation, and for combinations thereof.
Low-bypass turbofans tend to be louder and somewhat less fuel efficient than high-bypass designs, but are also more responsive, and are used for supersonic jet fighters and other high-performance applications. Low-bypass turbofans are also commonly configured for afterburning, in which additional fuel is introduced into an augmentor assembly downstream of the turbine, where it is ignited to provide substantially increased maximum thrust. Thrust augmentation is usually limited to short periods of high demand, on account of the increased operational stress and high rate of fuel consumption.
The gas turbine engine is highly adaptable, and also provides reliable and efficient power sources for specialized applications such as hydrocarbon fuel liquification, high-speed marine craft, armored vehicles and even hybrid cars. In each of these applications, performance ultimately rests upon the turbine's ability to precisely control the working fluid flow. As a result, there is a constant need for improved turbine vane designs, including designs which are adaptable to different turbine configurations and working fluid flows, including turning flows in the high- and low-pressure turbine sections, and in the transition regions between these sections.